Bonding structure and bonding method for cemented carbide element and diamond element, cutting tip and cutting element for drilling tool, and drilling tool

ABSTRACT

A cutting tip for a drilling tool includes a cemented carbide cutting base, a diamond element supported by the cutting base, and a bonding layer formed between the cutting base and the diamond element in order to bond them. The bonding layer includes diffusion layers and in which one or two or more metals selected from a group consisting of Fe, Ni, Co, Ti, Zr, W, V, Nb, Ta, Cr, Mo, and Hf diffuses into at least one of the diamond or the cement carbide.

CROSS-REFERENCE TO PRIOR APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/628,134, filed Jul. 25, 2003, now U.S. Pat. No. 7,261,753 whichclaims the benefit of Japanese Patent Application Nos. 2002-217433,filed Jul. 26, 2002, 2003-088130, filed Mar. 27, 2003, 2003-088131,filed Mar. 27, 2003, and 2003-088132, filed Mar. 27, 2003, all of whichare incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bonding method and bonding structurebetween a cemented carbide element and a diamond element. In addition,the present invention relates to a cutting tip, cutting element, and adrilling tool for drilling a well (winze) or the like.

2. Description of the Related Art

Drilling tools are used to drill oil wells and other types of wells. Asone such type of drilling tool, a drilling tool is known in which postsmade of superhard tungsten carbide alloy (below, referred to as“cemented carbide posts”) are attached to the distal surface of an ironalloy tool body in a predetermined arrangement by methods such asbrazing and shrinkage fitting, and cutting tips consisting of ultrahighpressure sintered diamond (below, referred to as “sintered diamond”) arebrazed to each of these cemented carbide posts. The drilling tool ismounted on the distal end of a pipe, the pipe is rotated while applyinga weight via the pipe in the drilling direction, and thereby drilling iscarried out by the cutting tips provided on the tool body.

Because the wettability of the sintered diamond that forms the cuttingtip with respect to the brazing filler metal is low, brazing using astandard brazing filler metal is difficult. In the drilling tooldisclosed in Japanese Unexamined Patent Application, First Publication,No. 2000-000686, an Au alloy brazing filler metal (melting point, 940°C.) having a composition including, for example, Cu at 20 to 40% by massand Ti at 0.5 to 10% by mass, with the remainder consisting of Au andunavoidable impurities, is used in order to braze a cutting tip to acemented carbide post. In addition, U.S. Pat. No. 6,248,447B1 disclosesa drilling tool in which cutting tips are formed by high heat resistantsintered diamond.

In recent years, requirements for labor saving, energy saving, and costreduction in the drilling operation are increasingly severe. Forexample, because the operating cost for one day during drillingoperations for development drilling for petroleum and the like isextremely high, it is necessary to complete the drilling operation in ashort time period by increasing the drilling speed in order to reducecosts.

In order to increase the drilling speed, both the load applied to thetool body and the rotation speed of the tool body should be increased.However, in both of these cases, a heavier load is applied to thecutting tips. The cemented carbide posts made of cemented carbides andthe cutting tips made of sintered diamond are bonded by the brazingdescribed above, and this bonding strength is not very high. Therefore,when an extremely heavy load is applied to the cutting tips, the cuttingtips may break off from the cemented carbide posts. In addition, whenthe drilling becomes high-speed, the heat due to drilling becomes high,and thereby it is possible that the cutting tips will break off from thecemented carbide posts because the brazing filler metal used to brazethe cutting tip can melt. Thus, conventionally it has not been possibleuse an extremely high drilling speed.

In consideration of the problems described above, it is an object of thepresent invention to increase the bonding strength between the cementedcarbide element and the diamond element.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a bonding structure between acemented carbide element and a diamond element. This bonding structureprovides a cemented carbide element, a diamond element, and a bondinglayer that is formed between the cemented carbide element and thediamond element in order to bond them. This bonding layer includes adiffusion layer in which at least one or two or more metals selectedfrom a group consisting of Fe, Ni, Co, Ti, Zr, W, V, Nb, Ta, Cr, Mo, orHf diffuses into at least one of the cemented carbide or the diamond.

According to this bonding structure, the cemented carbide element andthe diamond element are bonded more strongly because the bonding layerincludes the diffusion layer, and thereby the bonding strength betweenthe cemented carbide element and the diamond element is increased, andseparation becomes difficult. Moreover, applicability of the bondingstructure of the present invention is not limited to drilling tools, andcan be used in any field in which bonding between a diamond element anda cemented carbide element can be used.

The thermal expansion rates of the cemented carbide element and thediamond element are different. However, a relatively flexible bondinglayer is formed therebetween, and this bonding layer absorbs the stressapplied to the diamond element. Therefore, when returning to normaltemperature and pressure after heat treatment during bonding, the stressthat accumulates in the cemented carbide element and the diamond elementis absorbed by this bonding layer, the stress concentrates in thediamond element with difficulty, and cracks or the like occur in thediamond element with difficulty.

The bonding layer can include a diffusion layer in which at least one ofFe and Ni diffuses into diamond. Due to the favorable diffusion of Feand Ni into the diamond element and the cemented carbide element, a deepand relatively thick diffusion layer in the diamond element and thecemented carbide element can be formed. Therefore, there are theadvantages that the stress caused by the impact applied during drillingcan be easily relieved and cracks and the like occur with difficulty.

The bonding layer can include a diffusion layer in which Co diffusesinto the diamond, and a Co layer. Co is also an element that diffuseseasily into the diamond element and the cemented carbide element, butthe diffusion layer is hard. Thus, if the Co layer is caused to remainby not allowing the entire amount of the Co to diffuse, a crackingprevention effect and a impact relief effect can be obtained.

The bonding layer can include a diffusion layer in which one or two ormore metals selected from a group consisting of Ti, Zr, W, V, Nb, Ta,Cr, Mo, and Hf diffuse into at least one of the cemented carbide or thediamond. Although the diffusion of these metals into the diamond elementand the cemented carbide element is not very extensive, an advantageousbonding strength can be obtained. In addition, in the case of thesemetals, a hard carbide is formed between the metal and the diamond, andthus the bonding strength is increased because of this factor as well.

The diamond can be a high heat resistant sintered diamond including abinder phase of 0.1 to 15% by volume, where this binder phase is formedby one or two or more selected from the group consisting of carbonatesof Mg, Ca, Sr, and Ba, oxides of Mg, Ca, Sr, and Ba, complex carbonatesand complex oxide containing two or more thereof. In this case, it ispossible to increase the heat resistance of the diamond. Bonding of thehigh heat resistant sintered diamond to a cemented carbide element usinga standard brazing filler metal is difficult, but according to thestructure of the present invention, a high bonding strength can beobtained. Furthermore, in the present invention, it is possible to use astandard sintered diamond that includes cobalt.

When the cross-section in the transverse direction of the bonding layeris line analyzed using EPMA, the maximum value of the content of themetals in this cross-section is preferably 20 times or greater than theaverage value of the content of the metal in the region of the cementedcarbide element not influenced by the diffusion, and 100 times orgreater than the average value of the content of the metal in the regionof the diamond element not influenced by the diffusion. In this case,the bonding strength is increased due to the diffusion layer, and at thesame time the impact relief effect due to the bonding layer isadvantageous.

Another aspect of the present invention is a boding method for acemented carbide element and a diamond element. This bonding methodincludes a step in which a metal material including one or two or moremetals selected from a group consisting of Fe, Ni, Co, Ti, Zr, W, V, Nb,Ta, Cr, Mo, and Hf is interposed between the cemented carbide elementand the diamond element, and a step in which the cemented carbideelement, the diamond element, and the metal material are heated, adiffusion layer is formed in which the metal diffuses into at least oneof the cemented carbide element or the diamond element, and the cementedcarbide element and the diamond element are bonded.

The metal material can be a metal foil, metal powder, metal fibers, or acompound of metals. In brief, any form is suitable as long as the metalmaterial is thin, has a substantially uniform thickness, and can beinterposed between the cemented carbide element and the diamond element.This does not depend on the species of metal.

According to this bonding method, it is possible to bond at a highbonding strength a diamond element and a cemented carbide element, whichare naturally difficult to bond.

The metal material can include at a total of 70% by mass at least one ofFe and Ni. In this case, in the step for bonding the cemented carbideelement and the diamond element, preferably heating is carried out underconditions A (K) and B (GPa) that satisfy the following two equationssimultaneously, and a diffusion layer is formed by at least one of Feand Ni diffusing into the diamond. The formula for B is a simplifiedBarman-Simon equation.A>1175B>0.0027×A+0.81

The metal material can include Co at 70% by mass or greater. In thiscase, in the step of bonding the cemented carbide element and thediamond element, preferably heating is carried out under conditions A(K) and B (GPa) that satisfy the following two equations simultaneously,and a diffusion layer is formed by Co diffusing into the cementedcarbide, and a Co layer is formed.A>1175B>0.0027×A+0.81

The metal material can include at 70% by mass or greater one or two ormore of the metals selected from the group consisting of Ti, Zr, W, V,Nb, Ta, Cr, Mo, or Hf. In this case, in the step of bonding the cementedcarbide element and the diamond element, preferably heating is carriedout under conditions A (K) and B (GPa) that satisfy the following twoequations simultaneously, and a diffusion layer is formed by the metaldiffusing into at least one of the cemented carbide or the diamond.A>1175B>0.0027×A+0.81

The diamond can be a high heat resistant sintered diamond including abinder phase of 0.1 to 15% by volume, where this binder phase is formedby one or two or more selected from the group consisting of carbonatesof Mg, Ca, Sr, and Ba, oxides of Mg, Ca, Sr, and Ba, complex carbonatesand complex oxide containing two or more thereof. Bonding of the highheat resistant sintered diamond to a cemented carbide element using astandard brazing filler metal is difficult, but according to the methodof the present invention, a high bonding strength can be obtained.Furthermore, in the present invention, it is possible to use a standardsintered diamond that includes cobalt.

The metal material can have a first layer and a third layer that includeNi at 70% by mass or greater and a second layer interposed between thefirst layer and the third layer. The second layer includes at 70% bymass or greater carbon. In the step of bonding the cemented carbideelement and the diamond element, preferably heating is carried out underconditions A (K) and B (GPa) that satisfy the following two equationssimultaneously, and a diffusion layer is formed by the Ni diffusing intothe diamond of the diamond element.A>1175B>0.0027×A+0.81

In this case, the metal material can include Ni at 55 to 80% by mass asa whole and carbon in total at 20 to 45% by mass.

Another aspect of the present invention is a cutting tip for a drillingtool. This cutting tip includes a cemented carbide cutting base mountedon the post of the tool body of the drilling tool, a diamond elementsupported by the cutting base, and a bonding layer formed between thecutting base and the diamond element in order to bond them. The bondinglayer includes a diffusion layer in which one or two or more metalsselected from a group consisting of Fe, Ni, Co, Ti, Zr, W, V, Nb, Ta,Cr, Mo, and Hf diffuses onto at least one of the cemented carbide or thediamond. Other constituents are identical to those of the aspectsdescribed above.

Another aspect of the present invention is a cutting element for thedrilling tool. This cutting element includes a cemented carbide postmounted on the tool body of the drilling tool, a diamond elementsupported by the post, and a bonding layer formed between the post andthe diamond element in order to bond them. The bonding layer includes adiffusion layer in which one or two or more metals selected from a groupconsisting of Fe, Ni, Co, Ti, Zr, W, V, Nb, Ta, Cr, Mo, and Hf diffusesonto at least one of the cemented carbide or the diamond.

A cutting element for another drilling tool of the present inventionincludes a cemented carbide post mounted on the tool body of thedrilling tool, and any of the cutting tips described above, and thecutting base of the cutting tip is mounted on the post.

A cutting tip for another drilling tool of the present inventionincludes a cutting base mounted on the post of the tool body of thedrilling tool, a diamond element supported by the cutting base, and abonding layer formed between the cutting base and the diamond element inorder to bond them. The diamond element can be a high heat resistantsintered diamond including a binder phase of 0.1 to 15% by volume, wherethis binder phase is formed by one or two or more selected from thegroup consisting of carbonates of Mg, Ca, Sr, and Ba, oxides of Mg, Ca,Sr, and Ba, complex carbonates and complex oxide containing two or morethereof. A tungsten carbide cemented carbide that includes Co as abinding agent forms the cutting base, and the diffusion layer includesat least one of Ni or Fe.

An installation site is formed on the cutting base, where thisinstallation site has a pair of support surfaces facing towards theleading edge in the drilling direction with a space opened therebetween.The diamond element can have a shape conforming to that of theinstallation site, and is attached therein. In this case, the diamondelement can be supported by the pair of support surfaces, and therebythe impact applied to the diamond element can be relieved and thecutting force increased.

Another aspect of the present invention is a drilling tool. Thisdrilling tool includes a tool body, posts provided in plurality on thedistal surface of this tool body, and a cutting tip attached to each ofthe posts. The cutting tip is any of the cutting tips described above.In addition, the drilling tool can comprise a tool body and a cuttingelement provided in plurality on the distal surface of the tool body,and the cutting element can be any of the cutting elements describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective drawing showing an embodiment of the drillingtool of the present invention.

FIG. 2 is a side view of a cutting element that can be used in thedrilling tool shown in FIG. 1.

FIG. 3 is a perspective drawing of a cutting tip that can be used in thecutting element shown in FIG. 2.

FIG. 4 is a cross-sectional exploded drawing showing the bonding layerof the cutting tip of the present invention.

FIGS. 5A to 5C are longitudinal cross-sections showing anotherembodiment of the cutting tip.

FIG. 6 is a side view showing another embodiment of the cutting elementof the present invention.

FIG. 7 and FIG. 8 are graphs showing an example of the metalconcentration in a cross-section of the bonding layer.

FIG. 9 is a graph showing the thermal bonding conditions in the methodof the present invention.

FIG. 10 is a perspective drawing showing another example of the shape ofthe drilling tool of the present invention.

FIG. 11 is a graph showing the fluctuation of the carbon concentrationin the case of Ni diffusion.

FIG. 12 is a graph showing the fluctuation in tungsten concentration inthe case of Ni diffusion.

FIG. 13 and FIG. 14 are graphs showing the fluctuation of Niconcentration in the case of Ni diffusion.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Below, embodiments of the present invention will be explained withreference to the figures. However, the present invention is not limitedby the embodiments described below, and for example, the essentialelements can be appropriately combined.

FIG. 1 shows an example of the drilling tool of the present invention.This drilling tool 1 includes a tool body 2 having a substantially diskshape and a plurality of cutting elements 3 attached to the distalsurface of the tool body 2. The cutting elements 3 are attached by meanssuch as brazing or shrinkage fitting to the tool body 2, and aredisposed so as to have a predetermined arrangement that is rotationallysymmetrical with respect to the center of the tool body 2. The cuttingelements 3 in this example are disposed along a pair of intersectingperpendicular diameter lines with gaps provided therebetween. The toolbody 2 is formed, for example, by an iron alloy as stipulated by JIS SCH4 15.

As shown in FIG. 2, the cutting element 3 includes a cemented carbidepost 6 made of a cemented carbide and having, for example, a cylindricalshape, and a cutting tip 7 attached by brazing or the like to thesurface facing the drilling direction of the cemented carbide post 6.The material for the cemented carbide post 6 is not limited, and it canbe formed by a general tungsten carbide cemented carbide or the like.The shapes of the cemented carbide post 6 and the cutting tip 7 are notlimited to the above, and can be modified as necessary.

As shown in FIG. 3, the cutting tip 7 includes a cutting base (cementedcarbide element) 11 bonded to the cemented carbide post 6 and a diamondelement 12 attached to this cutting base 11, and a bonding layer 13 isformed therebetween. The cutting base 11 and the diamond element 12 arestrongly bonded by the bonding layer 13.

The cutting tip 7 of the present embodiment has a disk shape as a wholewith a uniform thickness. The cutting base 11 is substantially diskshaped, and one surface thereof (the bottom surface in FIG. 3) is abrazing surface for brazing to the cemented carbide post 6. Aninstallation site 11 a is formed on the upper surface of the cutting tip7 in FIG. 3 on the leading edge in the drilling direction.

The installation site 11 a is a fan-shaped recess centered on the centerof the cutting base 11, and has a uniform thickness. The thicknessthereof, which is equivalent to the thickness of the diamond element 12,is not limited, but preferably is about 10 to 60% of the thickness ofthe cutting base 11, and more preferably, 20 to 40%.

The installation site 11 a has a pair of V-shaped support surfaces 14whose opening widens towards the leading edge, and these supportsurfaces 14 receive and stop the impact applied to the diamond element12 during drilling. When the installation site 11 a has a supportsurface 14 with this type of wedge shape, the impact applied to thediamond element 12 is widely diffused over the cutting base 11, andthereby the strength against the impact is increased. In thisembodiment, the angle between the support surfaces 14 is not limited,but is preferably 45 to 108°, and more preferably 80 to 100°. The shapeof the installation site 11 a is not limited to the fan shape, and canbe a simple semicircular shape or the like.

The diamond element 12 has a shape conforming to that of theinstallation site 11 a, and is attached therein. Thereby, when thedrilling tool 1 advances along the axial direction while being rotatedaround its axis, only the diamond element 12 comes into contact with thedrilled material to drill the drilled material. Therefore, there islittle wear on the cutting base 11.

The cutting base 11 is formed by a cemented carbide such as a tungstencarbide cemented carbide using Co as the binding agent. For example, thecutting base 11 can be formed by a cemented carbide that includes Co at10% by mass as a binding agent with the remainder consisting of WC andunavoidable impurities. Because the cemented carbide has a high strengthand a high toughness, the cutting base 11 acts as a shock absorbing bodythat absorbs the thermal shock and the mechanical impact applied to thecutting tip 7 during the drilling operation.

The diamond element 12 is provided at the region on the cutting tip 7where wear occurs easily during the drilling operation. In the presentembodiment, the ratio of the length of the arc of the diamond element 12to the length of the semicircular arc on the leading edge of thedrilling direction of the cutting tip 7 is preferably 25 to 70%. Whenthe ratio is less than 25%, the cemented carbide contributes directly tothe drilling. When the ratio exceeds 70%, the ratio of the shockabsorbing portion becomes too small relatively, and the extremely highthermal and mechanical impact generated by the high-speed rotationoperation cannot be sufficiently absorbed. Thus, the occurrence of minorchipping particularly at the wear area increases. This ratio ispreferably 35 to 55%. However, this range is not limiting.

In the present embodiment, the diamond element 12 is preferably a highheat resistant sintered diamond including a binder phase of 0.1 to 15%by volume, where this binder phase is formed by one or two or moreselected from the group consisting of carbonates of Mg, Ca, Sr, and Ba,oxides of Mg, Ca, Sr, and Ba, complex carbonates and complex oxidecontaining two or more thereof. Among these, in particular a high heatresistant sintered diamond using magnesium carbonate as a binding agentis preferable because the sintering hardness is especially high and thewear resistance is advantageous. In addition, in the case of usingmagnesium carbonate as a binding agent, the diffusion of metal elementsinto the high heat resistant diamond is favorable, and thus has theadvantage that the time required for the bonding processing with thecutting base 11 becomes short.

The diamond element 12 can be formed by standard sintered diamond usingCo as the binding agent or a complex of a standard sintered diamond anda high heat resistant diamond.

The bonding layer 13 in the present embodiment includes a seconddiffusion layer S2 in which one or two or more metals selected from agroup consisting of Fe, Ni, Co, Ti, Zr, W, V, Nb, Ta, Cr, Mo, and Hfdiffuses into the cemented carbide of the cutting base 11, a firstdiffusion layer S1 in which metal diffuses into the diamond of thediamond element 12, and a metal layer 13A that remains including metalthat has not diffused.

In the case of metals having particularly good diffusion properties (Fe,Ni, Co), all of the metal may diffuse completely into the cutting base11 and/or the diamond element 12, and none of the metal layer 13A mayremain. When the diffusion of the metals is favorable for only one ofthe cemented carbide or the diamond, there will also be the case inwhich only one of the first diffusion layer S1 or the second diffusionlayer S2 is substantially formed (it does not matter whether or not themetal layer 13A is formed). Furthermore, any or all of the borderbetween the cutting base 11 and the second diffusion layer S2, theborder between the second diffusion layer S2 and the metal layer 13A,the border between the metal layer 13A and the first diffusion layer S1,and the border between the first diffusion layer S1 and the diamondelement 12 can be indistinct. The 30 present invention includes thesetypes of cases. The range of formation of the first diffusion layer S1and the second diffusion layer S2 can be investigated by carrying outline analysis using EPMA (Electron Probe Microanalyser) as describedbelow, or observation of the organization using a microscope.

FIG. 7 and FIG. 8 are graphs showing the concentration of the diffusedmetal in the bonding layer 13 and the area adjacent thereto. This typeof graph is obtained by carrying out line analysis of the cross-sectionof the bonding layer in the transverse direction using EPMA in thebonding layer 13 and the area adjacent thereto. FIG. 7 is a graph of thecase in which the metal layer 13A remains, and FIG. 8 is a graph of thecase in which the metal layer 13A does not remain.

In either case, the maximum value Nmax of the content of metal that hasdiffused into the bonding layer 13 is 20 times or greater than theaverage value N2 of the content in the region of the cutting base 11element not influenced by the diffusion, and 100 times or greater thanthe average value N1 of the content in the region of the diamond element12 not influenced by the diffusion. In this case, the bonding strengthis increased due to the first diffusion layer S1 and the seconddiffusion layer S2, and at the same time the impact relief effectattributable to the bonding layer 13 becomes advantageous.

Next, the fabrication method of the cutting tip 7 will be explained.

First, the cutting base 11 and the diamond element 12 are fabricated ina predetermined shape. The cutting base 11 is fabricated identically toa standard cemented carbide product. For example, a disk shaped cementedcarbide tip is formed by molding and sintering a base material powderfor the cemented carbide, and an installation site 11 a is formed byapplying a cutting operation to this cemented carbide tip.Alternatively, a base material powder for a cemented carbide can bedirectly molded and sintered into a disk shape having an installationsite 11 a.

An example of a method for producing the diamond element 12 will now beexplained. For example, in the case of using a diamond powder having anaverage particle diameter of 10 μm and a purity of 99.9% or greater anda MgCO₃ powder having an average particle diameter of 10 μm and a purityof 95% or greater as the base material powders, the MgCO₃ powder is madeinto a green compact having the desired shape by press molding the MgCO₃under a pressure of 100 MPa. Next, this green compact is charged into acapsule made of Ta and the diamond powder is placed on the green compactto fill the inside of the capsule. In this state, ultrahigh pressuresintering is carried out by placing the capsule into an ultrahighpressure belt sintering apparatus (an ultrahigh pressure sinteringapparatus standardly used in sintered diamond fabrication), and a blockof sintered diamond including MgCO₃ at 5% by volume is obtained. Thisultrahigh pressure sintering can be carried out, for example, by heatingat a temperature of 2250° C. under a pressure of 7.7 GPa maintained for30 minutes. However, the present invention is not limited to theseconditions.

After applying rough processing to the block of this sintered diamond bygrinding using a diamond grindstone, a diamond piece having the desiredshape is cut out by laser processing, and thereby the diamond element 12is obtained.

Next, a metal material is interposed between the cutting base 11 and thediamond element 12 obtained as described above, where this metalmaterial includes at 70% by mass or greater one or two or more metalsselected from a group consisting of Ti, Zr, W, V, Nb, Ta, Cr, Mo, or Hf,and the diamond element 12 is embedded in the installation site 11 a ofthe cutting base 11. A metal foil (for example, having a thickness of0.02 to 0.1 mm) is preferable as a metal material, but this is notlimiting, and a metal powder, a fiber metal, or a compound of metal canalso be used.

The cutting base 11, the metal foil, and the diamond element 12 thathave been temporarily assembled in this manner are set in an ultrahighpressure sintering apparatus such as an ultrahigh pressure beltsintering apparatus, heat processing is carried out at an ultrahightemperature and pressure, these elements are integrated by bonding, andthe cutting tip 7 is obtained. In this embodiment, the elements areheated to a temperature of 1500° C. under a pressure of 5.5 GPamaintained for 30 minutes. However, these ranges are not limiting.

Due to this heat processing, the components of the metal foil diffuseinto the cutting base 11 and the diamond element 12. Adjacent to theborder between the cutting base 11 and the metal foil, the seconddiffusion layer S1 wherein the components that form the metal foildiffuse into the cemented carbide, is formed. Adjacent to the borderbetween the diamond element 12 and the metal foil, the first diffusionlayer S1 wherein 25 the components that form the metal foil diffuse intothe diamond, is formed.

The thermal expansion rates of the cutting base 11 and the diamondelement 12 are different, but the metal layer 13 is formed therebetween,and this metal layer 13 acts as a stress relief material. Thereby, whenreturning to normal temperature and pressure after the heat processing,the stress that accumulates between the cutting base 11 and the diamondelement 12 is absorbed by the metal layer 13. Thereby, stressconcentrates in the diamond element 12 with difficulty, cracking and thelike between the cutting base 11 and the diamond element 12 occurs withdifficulty, and separation between the cutting base 11 and the diamondelement 12 occurs with difficulty. Next, the characteristics of eachmetal will be explained separately.

Fe and Ni

Fe and Ni diffuse into the diamond element 12 and the cutting base 11favorably. Thus, in the case of using Fe and/or Ni as the diffusingmetals, a relatively thick first diffusion layer S1 and second diffusionlayer S2 are formed inside the diamond element 12 and the cutting base11. Due to the presence of the thick diffusion layers S1 and S2, stressapplied to the diamond element 12 during drilling can be easilydiffused, and cracking and the like between the diamond element 12 andthe cutting base 11 occurs with difficulty. In the case of using Feand/or Ni as the diffusing metals, the metal layer 13A becomes thin ordisappears, and thus the concentration distribution of the Fe and/or Niadjacent to the bonding layer 13 tends towards the distribution shown inFIG. 8. In particular, in the case of Ni, the diffusion into the cuttingbase 11 is remarkable. Ni may diffuse across the entire area of thecutting base 11, and in this case, the effect of diffusing the stressapplied to the diamond element 12 during drilling is improved.

When the diamond element 12 and the cutting base 11 are bonded using Feand/or Ni as the metal material, the diamond element 12 and the cuttingbase 11 are temporarily assembled after interposing a metal materialtherebetween. Preferably either a 0.02 to 0.3 mm Ni foil, Fe foil, orNi—Fe alloy foil can be used as the metal material. When using a Ni—Fealloy foil, the diffusion becomes advantageous because it has a lowermelting point than the pure metals.

During the bonding, heating is carried out under conditions A (K) and B(GPa) that satisfy the following two equations simultaneously, and thediffusion layers S1 and S2 are formed by the Fe and/or Ni diffusing intothe diamond element 12 and the cuffing base 11.A>1175B>0.0027×A+0.81

The above range is the area in which the diamond is in thethermodynamically stable region represented by the Barman-Simon equationand the temperature at which the metal elements can diffuse. Thischaracteristic is identical for the other metal elements describedbelow.

The range shown by the diagonal line in FIG. 9 illustrates the ranges ofA and B described above. The range shown by the intersecting lines inFIG. 9 is a more preferable region, and this region is encompassed bythe following coordinates:

(1550 K, 5.0 GPa)

(1550 K, 8.0 GPa)

(2000 K, 8.0 GPa)

(2000 K, 6.2 GPa)

The thickness of the first diffusion layer S1 is preferably 0 to 0.2 mm,and more preferably 0.01 to 0.05 mm. The thickness of the seconddiffusion layer S2 is preferably 0 to 5 mm, and more preferably 0.1 to 3mm. When the thicknesses are within this range, the bonding strengthbetween the diamond element 12 and the cutting base 11 is strong and theimpact resistance can be made high.

Moreover, in this specification, the thickness of the diffusion layersS1 and S2 is defined as follows. Along the cross-section of the bondinglayer 13, the concentration of the metals is measured by EPMA or byAuger Electron Microscopy. In the case that the diffusion layer is thin,Auger Electron Microscopy is suitable. FIG. 7 and FIG. 8 are graphsshowing the concentration of metals starting from the diamond element12, through the bonding layer 13, and ending in the cutting base 11.

As shown in FIG. 7, in the case that the metal layer 13A remains in thebonding layer 13, the area of the portions (the diagonal portion) isfound. The area is obtained by respectively subtracting the metalconcentration N1 in the diamond element 12 not influenced by diffusionand the metal concentration N2 in the cutting base 11 not influenced bydiffusion from the regions outside the respective borders L1 and L2between the metal layer 13 and the diamond element 12 and the cuttingbase 11. The area from the borders L1 and L2 to the point encompassing80% of this surface area serves as the thickness of T1 and T2 of thediffusion layers S1 and S2.

In contrast, as shown in FIG. 8, in the case that a metal layer 13A doesnot remain in the bonding layer 13, the area of the portions (thediagonal portion) is found. The area is obtained by subtracting themetal concentration N1 in the diamond element 12 not influenced bydiffusion and the metal concentration N2 in the cutting base 11 notinfluenced by diffusion from both sides from the point of the maximumvalue Nmax of the metal concentration. The area from the point of themaximum value Nmax to the point encompassing 80% of this surface areaserves as the thickness of T1 and T2 of the diffusion layers S1 and S2.

The metal material is interposed between the diamond element 12 and thecutting base 11, and these elements are temporarily attached. In thecase that these elements are heated under an ultrahigh pressure of 5 to6 GPa at a temperature of 1400 to 1550° C. by an ultrahigh pressureheating apparatus, it can be confirmed that the diffusion layers of theNi and/or Fe are formed to a thickness of 0.01 to 0.05 mm on the diamondelement 12 side and to a depth of 0.1 to 3 mm on the cutting base 11side.

Ni and Graphite and/or Diamond

When using Ni as the diffusion element, the diffusion of Ni into diamondis favorable, and thus there are cases in which the Ni diffuses into thediamond element causing the volume of the diamond element to decease. Inthis case, carbon is introduced into the Ni object layers, and therebythe diffusion of the Ni into the diamond element can be suppressed.

In this case, a first layer and a third layer that include Ni at 70% bymass or greater is used as a metal material, and the second layerinterposed between the first layer and the third layer. The second layerserves as a layer that includes carbon at 70% by mass or greater, andconcretely, a graphite and/or diamond plate or powder are used.

The second layer is preferably set such that the metal material includesNi at 55 to 80% by mass of the whole, and includes the carbon at a totalof 20 to 45% by mass. More preferably, the metal material includes Ni at60 to 70% by mass of the whole, and includes the carbon at a total of 30to 40% by mass.

In the process in which a cemented carbide element and a diamond elementare bonded, heating is carried out under conditions A (K) and B (GPa)that satisfy the following two equations simultaneously, and thediffusion layer is formed by the Ni diffusing into the diamond of thediamond element.A>1175B>0.0027×A+0.81

More preferably, the range is encompassed by the following coordinates:

(1550 K, 5.0 GPa)

(1550 K, 8.0 GPa)

(2000 K, 8.0 GPa)

(2000 K, 6.2 GPa)

The thickness of the first diffusion layer S1, the thickness of thesecond diffusion layer S2, and the thickness of the metal layer 13A areidentical to the case of Ni diffusion described above.

In this manner, when using a metal material having a second layer, whichhas graphite and/or diamond as the main constituent, interposed betweenthe first layer and the third layer, which have Ni as the mainconstituent, carbon dissolves into the Ni during diffusion and bonding,and thereby diffusion of the solid solution into the diamond element issuppressed. Thus, because the diffusion of Ni into the diamond elementis suitably suppressed, a high diffusion bonding strength can beobtained while the reduction in volume of the diamond element due toexcess diffusion of Ni can be suppressed.

Co

Like Fe and Ni, Co also diffuses into the diamond element 12 and thecutting base 11 favorably. Thus, when using Co as the diffusing metal, acomparatively thick first diffusion layer S1 and second diffusion layerS2 are formed in the diamond element 12 and the cutting base 11. Due tothe presence of the thick diffusion layers S1 and S2, stress applied tothe diamond element 12 during drilling can be easily diffused, andcracking and the like between the diamond element 12 and the cuttingbase 11 occur with difficulty. In addition, Co has the advantage thatthe depletion into the diamond is more favorable than Fe and Ni.

However, when using Co, the first diffusion layer S1 and the seconddiffusion layer S2 are rather rigid, and thus preferably the bondingconditions are adjusted such that none of the Co diffuses, and the metallayer 13A including Co substantially remains.

When the diamond element 12 and the cutting base 11 are bonded using Coas a metal material, the diamond element 12 and the cutting base 11described above are temporarily attached with the metal materialinterposed therebetween. A 0.02 to 0.3 mm Co foil is preferably used asthe metal material.

While bonding, heating is carried out under conditions A (K) and B (GPa)that satisfy the following two equations simultaneously, and thediffusion layers S1 and S2 are formed by the Co diffusing into thediamond element 12 and the cutting base 11.A>1175B>0.0027×A+0.81

More preferably, the range is encompassed by the following coordinates:

(1550 K, 5.0 GPa)

(1550 K, 8.0 GPa)

(2000 K, 8.0 GPa)

(2000 K, 6.2 GPa)

The thickness of the first diffusion layer S1 is preferably 0.005 to 0.2mm, and more preferably 0.01 to 0.05 mm. The thickness of the seconddiffusion layer S2 is preferably 0.01 to 5 mm, and more preferably 0.02to 3 mm. The thickness of the metal layer 13A is preferably 0.01 to 0.2mm, and more preferably 0.05 to 0.1 mm. When the thicknesses are withinthe these ranges, the bonding strength between the diamond element 12and cutting base 11 is high, and the impact resistance can be made high.

Ti, Zr, W, V, Nb, Ta, Cr, Mo, or Hf

The diffusion of Ti, Zr, W, V, Nb, Ta, Cr, Mo, or Hf into the diamondelement 12 and the cutting base 11 is low in comparison to Fe, Ni, andCo. Thus, when using one or two or more metals selected from a groupconsisting of Ti, Zr, W, V, Nb, Ta, Cr, Mo, and Hf as the diffusingmetal, only a comparatively thin diffusion layer are formed.Nevertheless, they have properties that can guarantee that the bondingstrength will be high. In addition, because the metal layer 13A remainsin a comparatively thin state, the concentration distribution becomesthat shown in FIG. 7. Therefore, the impact relieving action due to themetal layer 13A is high. In addition, because hard carbide forms withthe diamond, the bonding strength is high due to this factor as well.

Ti, Zr, and W are all metals having high melting points (the meltingpoint is 1725° C. for Ti, 1857° C. for Zr, and 3382° C. for W), and themelting points for alloys of the 25 same are also high. When using thesethree metals, a tough carbide (Tic, ZrC, and WC) are formed particularlyin the first diffusion layer S1 due to the combining of the componentsof the metal foil and the components of the diamond element 12. Thus,the bonding strength between the diamond element 12 and the metal layer13A can be made remarkably high.

V, Nb, and Ta are also metals having high melting points (the meltingpoint is 1700° C. for V, 2467° C. for Nb, and 2850° C. for Ta), and themelting points for alloys thereof are also high. Among high meltingpoint metals, V, Nb, and Ta are metals that have a high ductility, andthe alloys thereof also have a high ductility. Therefore, the impactapplied to the bonding portion is absorbed by the metal layer 13A, andfailure due to fatigue in the bonding portion occurs with difficulty.

Mo, Cr, and Hf are all metals having extremely high melting points (themelting point is 2622° C. for Mo, 1905° C. for Cr, and 2207° C. for Hf),and they have superior heat resistance. The melting points for alloysthereof are also extremely high, and they also have superior heatresistance. Therefore, a high heat resistance can be obtained when usingMo, Cr, and Hf.

When bonding the diamond element 12 and the cutting base 11 using one ortwo or more metals selected from a group consisting of Ti, Zr, W, V, Nb,Ta, Cr, Mo, or Hf, the diamond element 12 and the cutting base 11described above are temporarily attached after a metal layer isinterposed therebetween. Preferably either a 0.02 to 0.3 mm pure metalfoil or alloy foil is used as the metal material. Because the meltingpoint is lower when using an alloy foil than when using a pure metal,the diffusion is advantageous. By overlying metal foils includingdifferent metal species, an effect is obtained that is similar to mixingpowders of different metal species. This method can be used for any ofthe metals.

While bonding, heating is carried out under conditions A (K) and B (GPa)that satisfy the following two equations simultaneously, and thediffusion layers S1 and S2 are formed by the Ti, Zr, W, V, Nb, Ta, Cr,Mo, or Hf diffusing into the diamond element 12 and the cutting base 11.A>1175B>0.0027×A+0.81

More preferably, the range is encompassed by the following coordinates:

(1550 K, 5.0 GPa)

(1550 K, 8.0 GPa)

(2000 K, 8.0 GPa)

(2000 K, 6.2 GPa)

The thickness of the first diffusion layer S1 is preferably 0.002 to0.05 mm, and more preferably 0.005 to 0.01 mm. The thickness of thesecond diffusion layer S2 is 0.005 to 0.5 mm, and more preferably 0.01to 0.05 mm. The thickness of the metal layer 13A is preferably 0.01 to0.2 mm, and more preferably 0.02 to 0.08 mm. When the thickness iswithin the these ranges, the bonding strength between the diamondelement 12 and cutting base 11 is high, and the impact resistance can bemade high.

Explanation of the Drilling Tool

The cutting tip 7 obtained as described above serves as the cuttingelement 3 brazed to the cemented carbide post 6. In addition, thedrilling tool 1 is obtained by mounting the cutting element 3 on thetool body 2.

In this drilling tool 1, the cutting base 11 and the diamond element 12are firmly bonded in the cutting tip 7. Thereby, it becomes possible todrill under the heavy load conditions of, for example, high-speeddrilling. The melting point of the metal or alloy that form the metallayer 13 is sufficiently high in comparison to the conventional brazingfiller metal, and the heat resistance of the bonded portion between thecutting base 11 and the diamond element 12 is increased in comparison tothe conventional technology. Thus it is possible to carry out drillingat a high-speed, which is impossible in a conventional drilling tool dueto the heat resistance problem of the brazing filler metal used therein.

When carrying out high-speed drilling, extremely high thermal andmechanical impact is applied to the cutting tip 7. The diamond element12 itself, which is used as the cutting tip 7, is remarkably hard, butcontrariwise, because it is brittle, chipping occurs easily when astrong impact is applied. In the diamond element 12, the advancement ofwear is significantly promoted due to the occurrence of chipping, and asa result, the service life is comparatively short.

As a result of the investigations of the inventors, it has beenunderstood that due to the relationship of the mounting position of thecutting tip 3 in the drilling tool 1, in the cutting tip 7 that formsthe cutting element 3, the wear due to drilling does not advance overthe entire surface of the cutting tip, but occurs locally at particularlocations on the leading face of the cutting tip. The wear on theremaining portion is simply minor wear that is dependent on the localwear. In addition, it has been understood that the size of the area inwhich the local wear occurs is equal to or less than 25% of the surfacearea of the leading face of the cutting tip.

In the present embodiment, a diamond element 12 having superior wearresistance is provided by being positioned on the cutting tip 7 in theregion where the wear occurs locally, while other portions are formed bya cemented carbide cutting base 11 that is shock absorbent. Thereby,local wear of the cutting tip 7 occurs with difficulty, minor chippingin the diamond element 12 due to impacts occurs with difficulty becausethermal and mechanical impacts applied to the cutting tip 7 duringdrilling are absorbed by the cutting base 11, and thus the service lifeof the cutting tip is improved.

When the ratio of the length of the diamond element 12 to the arc lengthof the cutting tip is less than 25%, the cemented carbide cutting base11 contributes directly to drilling, and wear of the cutting base 11 ispromoted. In contrast, when this ratio exceeds 70%, the relative ratioof the cutting base 11 that acts as a shock absorbing portion becomestoo small, the extremely high thermal and mechanical impact that occursduring high-speed rotation operation is not sufficiently absorbed, andthe occurrence of chipping in the diamond element 12 in particularincreases rapidly. Thus, the ratio of the diamond element 12 to thelength of the arc of the leading edge of the cutting tip 7 is preferably25 to 70%, and more preferably 35 to 55%.

In the embodiment described above, the cutting tip 7 was formed by acutting base 11 having a fan-shaped installation site 11 a and afan-shaped diamond element 12 including heat resistant sintered diamond,but this is not limiting. The elements that form the cutting tip 7 canhave other arbitrary shapes.

For example, in the cutting tip 7 in FIG. 5A, the disk shaped cuttingbase 11 and the disk shaped diamond element 12 are bound by a bondinglayer 13.

In the cutting tip 7 in FIG. 5B, a part thereof is a high heat resistantdiamond part 12 a including high heat resistant diamond, and theremaining part is a sintered diamond part 12 b including standardsintered diamond.

In the cutting tip 7 in FIG. 5C, the high heat resistant diamond part 12a is embedded in the sintered diamond part 12 b.

The shape of the drilling tool 1 is not limited to the shape shown inFIG. 1. For example, as shown in FIG. 10, a structure is possiblewherein the cutting tip 7 is attached so as to project from theperipheral surface of the tool body 2.

In the present embodiment, the bonding method and bonding structure ofthe cemented carbide element and the diamond element according to thepresent invention are shown as examples applied to the cutting tip 7 ofthe drilling tool 1, but this is not limiting. For example, as shown inFIG. 6, when used as a cutting tip, the cutting tip 7 a that is entirelyformed by a standard sintered diamond or a high heat resistant diamond,the present invention can be applied to the bonding between a cementedcarbide post 6 and a cutting tip 7 a in a cutting element 3.

In addition, the scope of application of the bonding method and thebonding structure between the cemented carbide element and the diamondelement according to the present invention is not limited only to theabove examples. Any arbitrary method or structure can be applied if thecemented carbide element and the diamond element can be bonded.

EXAMPLES

Experimental Example for Ni Diffusion

As a base material powder, a diamond powder having an average particlediameter of 10 μm and a purity of 99.9% or greater, and as a bindingagent, a MgCO₃ powder having an average particle diameter of 10 μm and apurity of 95% or greater were prepared.

The MgCO₃ powder was made into a green compact having predetermineddimensions by press molding under a pressure of 100 MPa. Next, thisgreen compact was charged into a capsule made of Ta, and the diamondpowder was placed on the green compact to fill the capsule. The capsulewas placed into a standard ultrahigh pressure belt sintering apparatus.A pressure of 7.7 GPa was applied to the capsule, a temperature of 2250°C. was maintained for 30 minutes, and ultrahigh pressure sintering wascarried out to form a plurality of circular sintered diamond elements.

This diamond element had a diameter of 11 mm and a thickness of 1.5 mm,and includes MgCO₃ at 4.0% by volume as a binding agent. The upper andlower surfaces of the diamond element were ground by a #200 diamondgrindstone to form a circular sintered diamond chip having a diameter of11 mm and a thickness of 1.25 mm. From the diamond chip, fan-shapeddiamond tips having a vertex of 90° were cut out using a laser, and a0.5 mm chamfering was applied to each of the corners.

At the same time, a circular cemented carbide tip having a diameter of12.5 mm and a thickness of 2.25 mm and a circular cemented carbide tiphaving a diameter of 12.5 mm and a thickness of 1.25 mm were prepared.These tips were formed by a cemented carbide including Co at 10% by massas the binding agent with the remainder consisting of WC and unavoidableimpurities. A fan-shaped recess having a shape conforming to thefan-shaped sintered diamond tip described above was formed in thecircular cemented carbide tip having a thickness of 1.25 mm.

A fan-shaped diamond tip was inserted into the fan-shaped recess of the1.25 mm thick cemented carbide tip after interposing a Ni foil, an Fefoil, or both a Ni foil and Fe foil having a thickness of 0.1 mmtherebetween. This was placed at the center between circular cementedcarbide tips having a thickness of 2.25 mm that were overlaid on bothsides. Between the three layers of the cemented carbide tips, a metalfoil like those described above was interposed. In this state, it wascharged set into a standard ultrahigh temperature and pressure beltsintering apparatus to be integrally bonded under a pressure of 5.5 GPaat a temperature of 1500° C. maintained for 30 minutes.

In order to expose the fan-shaped sintered diamond tip, the portion ofthe superhard part covering it was removed by using a #200 diamondgrindstone, then grinding processing was applied over the whole, and anexperimental example 1 having a diameter of 8 mm and a thickness of 3.5mm was produced.

The bonding interfaces of the experimental example were examined usingEPMA, and the diffusion layers were measured to a depth of 0.01 to 0.05mm from the bonding interface of the diamond element and to a depth of0.1 to 3.0 mm from the bonding interface of the cemented carbideelement. FIG. 11 is a graph sowing the fluctuation in the carbonconcentration adjacent to the bonding layer for Ni diffusion. FIG. 12 isa graph showing the fluctuation in the tungsten concentration adjacentto the bonding layer. FIG. 13 and FIG. 14 are graphs showing thefluctuation in the Ni concentration adjacent to the bonding layer. Asshown in FIG. 14, the diffused Ni was distributed through the surfacelayer portion of the cemented carbide element. The peak that occurs atthe 2.9 mm position in FIG. 14 is not related to diffusion.

Next, a WC powder having an average particle diameter of 1.5 μm, a Cr₃C₂powder having an average particle diameter of 2.3 μm, a ZrC powderhaving an average particle diameter of 1.3 μm, and a Co powder having anaverage particle diameter of 3.4 μm were prepared as base materialpowders. These base material powders were mixed in % by mass at ratiosof Co at 9%, Cr₃C₂ at 0.4%, ZrC at 0.2%, and the remainder WC, and thenthey were wet-mixed in a bowl mill for 72 hours. After drying, thismixture was press molded into a green compact under a pressure of 0.1GPa, and this green compact was sintered in a vacuum at 0.13 Pa and amaintained at a temperature of 1400° C. for 1 hour. Thereby, a cementedcarbide post was fabricated that has a maximum diameter of 15 mm, abottom surface diameter of 13 mm, a length of 20 mm, and has the shapeshown in FIG. 2. Experimental example 1 was set on the cemented carbidepost described above after interposing a composition (in % by mass) ofNi-14% Cr-3.5% B-4.0% Si-4.5% Fe-0.7% C alloy brazing filler metalhaving a thickness of 0.35 mm, and bonded by brazing at 1100° C. Asshown in FIG. 1, cemented carbide posts were attached to a total of 16recesses having a depth of 8 mm arranged in a cross-shape on the 240 mmdiameter distal surface of the bit body formed by a steel alloy asstipulated in JIS SCM 415 after interposing a Cu alloy brazing fillermetal having a composition of Cu-40% Ag-6% Sn-2% Ni and a thickness of35 mm. The drilling tool was fabricated by brazing at 800° C.

Experimental Example for Co Diffusion

As a base material powder, a diamond powder having an average particlediameter of 10 μm and a purity of 99.9% or greater, and as a bindingagent, a MgCO₃ powder having an average particle diameter of 10 μm and apurity of 95% or greater were prepared.

The MgCO₃ powder was made into a green compact having the predetermineddimensions by press molding under a pressure of 100 MPa. Next, thisgreen compact was charged into a capsule made of Ta and the diamondpowder was placed on the green compact to fill the capsule. The capsulewas placed into a standard ultrahigh pressure belt sintering apparatus.A pressure of 7.7 GPa was applied to the capsule, a temperature of 2250°C. was maintained for 30 minutes, and ultrahigh pressure sintering wascarried out to form a plurality of circular sintered diamond elements.

This diamond element has a diameter of 11 mm and a thickness of 1.5 mm,and as a binding agent includes MgCO₃ at 4.0% by volume. The upper andlower surfaces of the diamond element were ground by a #200 diamondgrindstone to form a circular sintered diamond chip having a diameter of11 mm and a thickness of 1.25 mm. From the diamond chip, fan-shapeddiamond tips having a vertex of 90° were cut out using a laser, and a0.5 mm chamfering was applied on each of the corners.

At the same time, a circular cemented carbide tip having a diameter of12.5 mm and a thickness of 2.25 mm, and a circular cemented carbide tiphaving a diameter of 12.5 mm and a thickness of 1.25 mm were prepared.These tips were formed by a cemented carbide including Co at 10% by massas the binding agent with the remainder consisting of WC and unavoidableimpurities. A fan-shaped recess having a shape conforming to thefan-shaped sintered diamond tip described above was formed in thecircular cemented carbide chip having a thickness of 1.25 mm.

A fan-shaped diamond tip was engaged in the fan-shaped recess of the1.25 mm thick cemented carbide tip after interposing a Co foil having athickness of 0.1 mm therebetween. This was placed at the center betweencircular cemented carbide chips having a thickness of 2.25 mm disposedon both sides. These bonding surfaces were overlaid above and belowafter interposing this Co foil. In this state, they were placed into astandard ultrahigh temperature and pressure belt sintering apparatus tobe integrally bonded under a pressure of 5.5 GPa at a temperature of1450° C. maintained for 30 minutes.

In order to expose the fan-shaped sintered diamond tip (the drillingwear portion), the integral superhard part covering it was removed byusing a #200 diamond grindstone, then grinding processing was appliedover the whole, and an experimental example 2 having a diameter of 8 mmand a thickness of 3.5 mm was produced.

The bonding interfaces of the experimental example 2 were examined usingEPMA, the 0.05 mm Co metal layer was observed at the bonding interface,and the diffusion layers were measured to a depth of 0.01 to 0.05 mmfrom the bonding interface of the diamond element and to a depth of 0.1to 3.0 mm from the bonding interface of the cemented carbide element.

Next, a WC powder having an average particle diameter of 1.5 μm, a Cr₃C₂powder having an average particle diameter of 2.3 μm, a ZrC powderhaving an average particle diameter of 1.3 μm, and a Co powder having anaverage particle diameter of 3.4 μm were prepared as base materialpowders. These base material powders were mixed in % by mass at ratiosof Co at 9%, Cr₃C₂ at 0.4%, ZrC at 0.2%, and the remainder WC, and thenthey were wet-mixed in a bowl mill for 72 hours. After drying, thismixture was press molded into a green compact under a pressure of 0.1GPa, and this green compact was sintered in a vacuum at 0.13 Pa and atemperature of 1400° C. maintained for 1 hour. Thereby, a cementedcarbide post was fabricated that has a maximum diameter of 15 mm, abottom surface diameter of 13 mm, a length of 20 mm, and has the shapeshown in FIG. 2. Experimental example 2 was set on the cemented carbidepost described above after interposing a Ni alloy brazing filler metalhaving a thickness of 0.35 mm and a composition (in % by mass) of Ni-14%Cr-3.5% B-4.0% Si-4.5% Fe-0.7% C, and bonded by brazing at 1100° C. for5 minutes. As shown in FIG. 1, cemented carbide posts were attached to atotal of 16 recesses having a depth of 8 mm arranged in a cross-shape onthe 240 mm distal surface of the bit body formed by a steel alloy asstipulated in JIS SCM 415 after interposing a Cu alloy brazing fillermetal having a thickness of 35 mm and a composition of Cu-40% Ag-6%Sn-2% Ni. The drilling tool was fabricated by brazing at 800° C.

Experimental Example for Ta diffusion

As a base material powder, a diamond powder having an average particlediameter of 10 μm and a purity of 99.9% or greater, and as a bindingagent, a MgCO₃ powder having an average particle diameter of 10 μm and apurity of 95% or greater were prepared.

The MgCO₃ powder was made into a green compact having the predetermineddimensions by press molding under a pressure of 100 MPa. Next, thisgreen compact was charged into a capsule made of Ta and diamond powderwas placed on the green compact to fill the capsule. The capsule wasplaced into a standard ultrahigh pressure belt sintering apparatus. Apressure of 7.7 GPa was applied to the capsule, a temperature of 2250°C. was maintained for 30 minutes, and ultrahigh pressure sintering wascarried out to form a plurality of circular sintered diamond elements.

This diamond element has a diameter of 11 mm and a thickness of 1.5 mm,and as a binding agent includes MgCO₃ at 4.0% by volume. The upper andlower surfaces of the diamond element were ground by a #200 diamondgrindstone to form a circular sintered diamond chip having a diameter of11 mm and a thickness of 1.25 mm. From the diamond chip, fan-shapeddiamond tips having a vertex of 90° were cut out using a laser, and a0.5 mm chamfering was applied on each of the corners.

At the same time, a circular cemented carbide tip having a diameter of12.5 mm and a thickness of 2.25 mm, and a circular cemented carbide chiphaving a diameter of 12.5 mm and a thickness of 1.25 mm were prepared.These tips were formed by a cemented carbide including Co at 10% by massas the binding agent with the remainder consisting of WC and unavoidableimpurities. A fan-shaped recess having a shape conforming to thefan-shaped sintered diamond tip described above was formed in thecircular cemented carbide tip having a thickness of 1.25 mm.

A fan-shaped diamond tip was engaged in the fan-shaped recess of the 1mm cemented carbide tip after interposing a Ta foil having a thicknessof 0.05 mm therebetween. This was placed at the center between circularcemented carbide tips having a thickness of 2.25 mm disposed on bothsides, and these bonding surfaces were overlaid above and below afterinterposing this metal foil. In this state, they were set into astandard ultrahigh temperature and pressure belt sintering machine to beintegrally bonded under a pressure of 6 GPa at a temperature of 1500° C.maintained for 30 minutes.

In order to expose the fan-shaped sintered diamond tip, the integralsuperhard part covering it was removed by using a #200 diamondgrindstone, then grinding processing was applied over the whole, and anexperimental example 3 having a diameter of 8 mm and a thickness of 3.5mm was produced.

The bonding interfaces of the experimental example 3 were examined usingEPMA, the 0.03 mm Ta metal layer was observed at the bonding interface,and the diffusion layers were measured to a depth of 0.005 to 0.01 mmfrom the bonding interface of the diamond element and to a depth of 0.01to 0.05 mm from the bonding interface of the cemented carbide element.

Next, a WC powder having an average particle diameter of 1.5 μm, a Cr₃C₂powder having an average particle diameter of 2.3 μm, a ZrC powderhaving an average particle diameter of 1.3 μm, and a Co powder having anaverage particle diameter of 3.4 μm were prepared as base materialpowders. These base material powders were mixed in % by mass at ratiosof Co at 9%, Cr₃C₂ at 0.4%, ZrC at 0.2%, and the remainder WC, and theywere wet-mixed in a bowl mill for 72 hours. After drying, this mixturewas press molded into a green compact under a pressure of 0.1 GPa, andthis green compact was sintered in a vacuum at 0.13 Pa and a temperatureof 1400° C. maintained for 1 hour. Thereby, a cemented carbide post wasfabricated that has a maximum diameter of 15 mm, a bottom surfacediameter of 13 mm, a length of 20 mm, and has the shape shown in FIG. 2.Experimental example 3 was set on the cemented carbide post describedabove after interposing a Ni alloy brazing filler metal having athickness of 0.35 mm and a composition (in % by mass) of Ni-14% Cr-3.5%B-4.0% Si-4.5% Fe-0.7% C, and bonded by brazing at a temperature of1100° C. for 5 minutes. As shown in FIG. 1, cemented carbide posts wereattached to a total of 16 recesses having a depth of 8 mm arranged in across-shape on the 240 mm distal surface of the bit body formed by asteel alloy as stipulated in JIS SCM 415 after interposing a Cu alloybrazing filler metal having a thickness of 0.35 mm and a composition ofCu-40% Ag-6% Sn-2% Ni. The drilling tool was fabricated by brazing at800° C.

FIELD OF INDUSTRIAL APPLICABILITY

The bonding structure between the cemented carbide element and thediamond element according to the present invention can be applied, forexample, to a cutting tip of a drilling tool. In this case, the cuttingtip shows superior resistance to chipping under high-speed revolutionoperation conditions of the drilling tool, and exhibits superior wearresistance over a long period of time. Therefore, reduction of drivepower, energy reduction, and cost reduction in the drilling operationcan be promoted.

1. A cutting tip, comprising: a cemented carbide cutting base; a diamondelement supported by said cutting base; and a bonding layer formedbetween said cutting base and said diamond element in order to bondthem; wherein said bonding layer includes a diffusion layer in which oneor two or more metals selected from a group consisting of Fe, Ni, Co,Ti, Zr, W, V, Nb, Ta, Cr, Mo, and Hf diffuses into at least one of saidcemented carbide or said diamond, and when a cross-section in atransverse direction of said bonding layer is line analyzed using EPMA,the maximum value of a content of said metals in said cross section is20 times or greater than an average value of a content of said metals ina region of the cemented carbide element not influenced by thediffusion, and 100 times or greater than an average value of a contentof said metal in a region of said diamond element not influenced by thediffusion.
 2. A cutting tip according to claim 1, wherein said bondinglayer includes a diffusion layer in which at least one of Fe and Nidiffuse into said diamond.
 3. A cutting tip according to claim 1,wherein said bonding layer includes a diffusion layer in which Codiffuses into said diamond, and a Co layer.
 4. A cutting tip accordingto claim 1, wherein said bonding layer includes a diffusion layer inwhich one or two or more metals selected from a group consisting of Ti,Zr, W, V, Nb, Ta, Cr, Mo, or Hf diffuses into at least one of saidcemented carbide or said diamond.
 5. A cutting tip according to claim 1,wherein said diamond element is a high heat resistant sintered diamondincluding a binder phase of 0.1 to 15% by volume, where said binderphase is formed by one or two or more selected from the group consistingof carbonates of Mg, Ca, Sr, and Ba, oxides of Mg, Ca, Sr, and Ba,complex carbonates and complex oxide containing two or more thereof.